The present invention relates to the attachment of a multi-flow turbojet engine to an aircraft by suspending it from the wing structure or any other structure thereof by means of a pylon.
A multi-flow turbojet engine comprises a turbojet consisting of a gas turbine engine driving a fan. The invention relates to the fan engines situated at the front. The air compressed by the fan is split into two or more concentric flows; an internal primary flow passes through the gas turbine engine being heated up in the combustion chamber then expanded in the turbine section which drives the air compression sections, before being discharged into the atmosphere. The other flow or flows remain cold; they are discharged directly into the atmosphere or alternatively are mixed beforehand with the gases of the primary flow and provide most of the thrust. The bypass ratio, which is the ratio between the flow rate of cold air and the flow rate of hot gas, in the case of engines for civil aviation is relatively high, and at the present time is commonly of the order of five to six. This type of engine comprises two structural casing elements via which the loads are transmitted between the aircraft and the engine, one at the front in the continuation of the fan casing, that forms the casing known as the intermediate casing, and the other at the rear, forming the exhaust casing. The engine is attached to the wing structure on two transverse suspension planes passing through these structural elements.
The attachment pylon or strut is a rigid structural component that forms the connection interface between the engine and the wing structure of the aircraft and, in particular, is connected to the engine in these two planes. It allows load to be transmitted from the engine to the structure of the aircraft. It also has the function of guiding auxiliaries. The pylon is generally an elongate structure of rectangular cross section of the box structure type. It is formed by assembling upper and lower spars and lateral panels joined together via transverse ribs. It comprises, on the one hand, means of attachment to the engine and, on the other hand, on its upper part, means of attachment to the wing structure of the airplane.
This type of engine attachment is used and works satisfactorily for engines with the kind of bypass ratio mentioned hereinabove.
Technological advances in engine technology lead to an increase in the bypass ratio with a view to doubling this in the future. This will result in a structural modification that could make the current means of attachment less suitable. This is because the diameter of the fan is increased while that of the part involving the primary flow does not progress to the same extent and remains at the same order of magnitude. The loads introduced along the axis of this type of engine, particularly when the aircraft is taking off, are then greater even though the central part downstream of the fan remains relatively flexible. No solution has been found nor even is any solution possible for making this more rigid. This results in deformations along the axis, bending, and misalignment of the rotary elements, all of this reducing engine performance.